well, in addition to asking here, the thing to do is to go into the shop. check out their standards of clenliness. (especially the bathroom...the condition of the bathroom says a lot about a place) and ensure that they use single use tattoing needles, that their artists are wearing gloves / changing gloves...etc...

and very important, unless they have full portfolios online, go in and look at artist portfolios. perhaps book a consultation (free) to talk to an artist about what you are looking for. and find the best artist there for the sort of work you want done.